Although host-malarial parasite interaction has been studied extensively in recent years, there has been very little work done on the interaction between the host cells and Babesia due to several technical problems. Recent development in Babesia culture systems has overcome these technical problems and now enable us to study the interaction between host cells and Babesia in vitro. The overall objective of the proposed research is to study the mechanism of erythrocyte invasion and the effects of antibodies on Babesia during the invasion processes. This will be accomplished by utilizing culture systems of B. bovis and B. cannis with examination by transmission and scanning electron microscopy of host-Babesia interaction. These results will be compared with those of Plasmodium. Since many similarities exist between these parasites, the proposed studies will enhance the understanding of both diseases.